Conventionally, an ion implanting apparatus disclosed in Patent Document 1 is proposed to prevent an ion having a different energy from a desirable energy or a neutral particle from mixing into an ion beam in an ion implantation.
As shown in FIG. 1A, an ion implanting apparatus A100 serves to select only an ion of a desirable type from an ion beam IB extracted at a certain voltage from an ion source A1 by means of an analyzing magnet A2 and to cause the ion beam IB to pass through an electrostatic accelerating tube A3 via the analyzing magnet A2, thereby obtaining a desirable energy, and furthermore, to deflect the ion beam IB to be incident on a target T at a predetermined incident angle.
The electrostatic accelerating tube A3 will be described in detail. As shown in FIG. 1B, an accelerating/decelerating electrode A4, a deflecting electrode A5 and a counter electrode A6 are provided in this order from an upstream of the ion beam IB. The deflecting electrode A5 is constituted by a first deflecting electrode A51 and a second deflecting electrode A52. The first deflecting electrode A51 is provided in parallel with a travelling direction of the ion beam IB which is not deflected. The second deflecting electrode A52 has an upstream portion which is parallel with the travelling direction of the ion beam IB that is not deflected and a downstream portion which is formed in parallel with a travelling direction of the ion beam IB subjected to the deflection and takes a substantially dogleg shape. Electric potentials of the first deflecting electrode A51 and the second deflecting electrode A52 are caused to be different from each other, thereby accelerating/decelerating and deflecting the ion beam IB. As a result, the ion beam IB is caused to have a desirable energy and an ion having the other energy is separated through the deflection. Consequently, only the ion beam IB having the desirable energy can be incident on the target T.
In the case in which the ion beam IB is accelerated/decelerated in the ion implanting apparatus A100, however, there is a problem. In other words, a deflecting center position C to be an intersection point of an optical axis LS of a straight part in the ion beam IB which is not deflected and an optical axis LE of a straight part in the ion beam IB subjected to the deflection is shifted so that a center position of the ion beam IB which is incident on the target T is shifted from a desirable place.
More specific description will be given by taking, as an example, an ion implantation in the case in which the ion beam IB is incident on the target T substantially vertically as shown in FIG. 2. FIG. 2B shows a normal state in which the acceleration/deceleration is not carried out but the ion beam IB is incident on the target T with the energy of the extracted ion beam IB maintained. At this time, a center of the ion beam IB is set to be incident on that of the target T.
On the other hand, in the case in which the ion beam IB shown in FIG. 2A is accelerated, that is, the ion beam IB is incident, on the target T, with a greater energy than the energy of the extracted ion beam IB, the deflecting center position C is changed toward an upstream side of the ion beam IB as compared with the normal state shown in FIG. 2B. As a result, the center of the ion beam IB which is incident on the target T is shifted slightly in a deflecting direction of the ion beam IB.
In the case in which the ion beam IB shown in FIG. 2C is decelerated, that is, the ion beam IB is incident, on the target T, with a smaller energy than the energy of the extracted ion beam IB, furthermore, the deflecting center position C is greatly changed toward a downstream side of the ion beam IB as compared with the normal state shown in FIG. 2B. As a result, the center of the ion beam IB which is incident on the target T is greatly shifted in an anti-deflecting direction of the ion beam IB.
A simulation condition in FIGS. 2A to 2C is set in such a manner that an extracting voltage of the ion beam IB is 30 kV, and the ion beam IB is accelerated/decelerated through the electrostatic accelerating tube A3 to have a desirable energy, for example, 60 keV in the acceleration, 30 keV in the normal state and 1 keV in the deceleration and is then irradiated perpendicularly to a surface of the target T.
In the case in which the ion beam IB is particularly decelerated, thus, the deflecting center position C is shifted greatly. For this reason, the center position of the ion beam IB which is incident on the target T is also shifted. Consequently, it is difficult to carry out a desirable ion implantation.
If an electric potential of the deflecting electrode A5 is regulated to adjust the incident position of the ion beam IB on the target T into a desirable position in the ion implanting apparatus A100, moreover, an angle of the incidence on the target T is varied as shown in FIG. 3. For this reason, it is still impossible to carry out the desirable ion implantation.